won't that make search engines index your page as if it was perfectly up but serving your weird down page?
– Paul TarjanAug 26 '09 at 22:26

@Paul : I have to admit I don't know for sure ; I've put <meta name="robots" content="noindex, follow" /> in down.html as a security measure, but I'm not sure what a bot would do : I've never seen the content of my down.html page on google, that's for sure, and I've never noticed anything "bad" for the other pages ;; but my maintenance operations are rare, and never lasted more than 3 hours ;; and my website is not big/famous, so not indexed too often... ;; Still, if someone sees a way to make this better, I'm definitly interested (would be nice to provide an answer, and get one myself !) ;-)
– Pascal MARTINAug 26 '09 at 22:33

You should add the [R=503] status to the RewriteRule to signify a temporary maintenance condition.
– Martijn HeemelsApr 12 '11 at 9:51

@MartijnHeemels: [R=503] doesn't work on my Apache, because it requires ErrorDocument 503 directive. With ErrorDocument Apache behaves a little differently to what was suggested above, by redirecting user to down.html rather than just showing down.html for any request.
– DaeMar 23 '14 at 18:52

I don't see anyone using the Retry-After header. I've read (but don't have the link anymore as I read it a while ago) that you should use a 503 in combo with a Retry-After n (n = number of seconds to try again in; 3600 is an hour) header. If you use the 503 and the Retry-After in combo, especially on your robots.txt/sitemap it should not mess with links and page rank for SEO if you don't leave it like that for a long time.